The proposed reseach is concerned with the development of semantic organization in young children, with the particular aim of elucidating the bases for the alternative modes of thought that have been variously labeled pre-operational/concrete operational, ikonic/symbolic or stimulus/response-mediated. One series of experiments explores the possibility that the features attended to by a young child, and therefore most strongly represented in his memory, are not those on which an adult has learned to rely. These experiments use a cued recall paradigm to assess the relative importance of categorical, perceptual, and locational relationships as encoding and retrieval dimensions for kindergarten, grade school, and adult subjects as a function of mode of stimuli presentation (i.e., visual or verbal). One explanation for the young child's apparent reliance on context and co-occurrence as bases for association is that he has difficulty analyzing his experiences into features according to which words and objects can be simultaneously compared and contrasted. The special relationship between opposites represents the simplest case of the isolation of a feature; thus, children's understanding of opposition can be used as an index of their progress in building a semantic feature system. The second series of experiments uses a number of experimental techniques to examine the development of semantic connections between opposites as a function of the nature of the opposition, both in terms of meaning and in terms of formal structure. The third series of experiments examines the acquisition of one particular semantic distinction, that for gender. It relates the child's automatic encoding in terms of sex appropriateness (as measured by a novel auditory "verbal Stroop" technique) to his or her adoption of a traditional sexual identity as measured by behavioral indices. The verbal Stroop task is particularly suitable for use with very young children, and can be used as a tool for exploring the structure of their knowledge of other semantic domains as well. This research has direct implications for curriculum planning for the early school years.